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Year 12 Chemistry > Food chemistry > Flashcards

Food chemistry Flashcards

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1
Q

what are the two functional groups found in amino acids?

A

amino (-NH2) and carboxylate group (COOH)

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2
Q

How many amino acids are found in the body

A

20

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3
Q

Why are amino acids called alpha amino acids?

A

The amino, carboxylate and R groups are all attached to the same C atom. All human amino acids are alpha amino acids

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4
Q

What are essential amino acids

A

Must be provided directly through the proteins in the diet as human cells cannot synthesis them

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5
Q

What are non essential amino acids

A

Can be manufactured in the body from the dietary components.

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6
Q

Why are amino acids soluble in water

A

A a consequence of the polar amino and carboxylate functional groups

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7
Q

Why are amino acids amphiprotic

A

The amino group can act as a base and the carboxyl group can act as an acid

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8
Q

How are proteins formed

A
  • Proteins are polymers formed by condensations reactions between amino acids.
  • The amino group of one amino acid reacts with the carboxyl group of an adjacent amino acid
  • A covalent bond is formed between them and a molecule of water is eliminated
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9
Q

What is the peptide linkage

A

The CONH group of atoms that links the constituent amino acid

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10
Q

What is the primary structure of proteins

A

The order of amino acids joined together in the polypeptide with peptide links between them (covalent bonds)

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11
Q

What is the secondary structure of proteins

A
  • Parts of the chain can attract each other creating 3D shapes such as coiling and pleating.
  • H bonds between polar NH group in one peptide like and the polar C=O in another peptide link can form at regular intervals
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12
Q

What is the tertiary structure of a protein?

A

-Some side groups are capable of forming bonds themselves with groups elsewhere on the protein chain

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13
Q

Types of bonds in tertiary structure?

A
  • dispersion forces between non polar side chains
  • H bonds between side chains (amino and c=O-NH2)
  • Ion dipole between Nh3+ and cooh
  • Ionic between NH3+ and COO-
  • Di sulphide bridge (covalent) between non adjacent cysteine residues
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14
Q

What is the quaternary structure of a protein?

A

Multiple polypeptides chains held together with same bonding as tertiary structure

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15
Q

What is the general formula for a carb

A

Cx(H2O)y with H:0 ratio always 2:1

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16
Q

Why are monosaccharides soluble in water

A

They contain a number of polar hydroxy function groups (OH) enabling them to form hydrogen bonds with water.

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17
Q

What are the three most common monosaccharides

A

fructose, glucose and galactose with C6H12O6

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18
Q

How many chiral centres do glucose and lactose have

A
  1. This different causes molecules to behave differently in living organisms
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19
Q

Difference in glucose and galactose

A

Position of OH on 5th carbon has been flipped

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20
Q

Why is glucose the main source of energy

A

Glucose and its polymer starch is more rapidly digested that other forms of foods (ie lipids and proteins)

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21
Q

What is a disaccharide

A

Carbohydrate formed when two monosaccharides undergo a condensations reaction (with water eliminated)

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22
Q

Maltose, sucrose, lactose

A

Glucose plus glucose
Fructose and sucrose
galactose and lactose

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23
Q

Polysaccharides

A

Polymer carbohydrates made by linking monosaccharides into a chain

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24
Q

Why are polysaccharides insoluble in water?

A

Most of the hydroxy polar functional groups are used for other links in the polymer. This the large polymer has non polar characteristics.

25
Q

Three most biological important polysaccharides

A

Glycogen starch and cellulose

26
Q

Function of glycogen

A

Found in animals and acts as a glucose storage molecules. As energy is required glycogen is hydrolysed to yield glucose for respiration

27
Q

Compare bp of glycogen

A

Polymer chains are less closely packed due to branching. Thus intermolecular forces are weaker (dispersion) therefore soft and lower mp

28
Q

Function of starch

A

Glucose storage molecule in plants

29
Q

Types of lipids

A

fats and oils

30
Q

What are the constituents of fats and oils

A

C, H and small amounts of O occasionally

31
Q

Difference between fats and oils

A

they have very similar chemical structures and are distinguished based on their physical states at room temperatures. Fats are solids. Oils are lipids

32
Q

How are fats and oils formed

A

Condensation reaction between a single molecule of glycerol and three molecules of fatty acids. Called triglycerides

33
Q

Compare reactivity of saturated and polyunsaturated fatty acids

A

saturated fatty acids are least reactive and accumulate in the body while unsaturated fatty acids are the most reactive and have the least accumulation in body cells

34
Q

Physical properties compared of saturated and polyunsaturated fatty acids

A

FA chains are very closely packed, stronger dispersion forces, solid at room temp with a higher mp.
For unsaturated fatty acids the chains are far apart due to unsaturation, weaker dispersion forces, oil at room temperature and they have the lowest melting point.

35
Q

What are essential fatty acids

A

Some polyunsaturated fats cannot be manufactured by the body and must be obtained from food.

36
Q

What is the polarity and solubility of lipids

A

Most lipids are essentially non polar and insoluble in water. But they dissolve in non polar solvents

37
Q

Difference between omega 3 and omega 6 fatty acids

A
  • Unsaturated fatty acids with a double bond on the third last carbon atom in the hydrocarbon chain are classified as omega 3 fatty acids.
  • In the double bond is on the sixth last carbon atom, they are classified as omega 6 fatty acids
38
Q

What are the two classifications of vitamins

A

Water soluble and fat soluble vitamins

39
Q

Implication of water soluble vitamins

A

Excreted by the body if they are not used, so they must be consumed as a regular part of the diet.

40
Q

Implication of fat soluble vitamins

A

Can be stored in the body in fatty tissue for a long period of time
Dangerous to take excessive quantities as the body does not easily dispose of them

41
Q

Are these vitamins considered essential

A

Yes as humans cannot synthesise them except for biotin (vitamin b&) and vitamin D (synthesised in skin after expose to UV radiation)

42
Q

Difference between macronutrients and micronutrients

A
  • The body requires macronutrients in relatively large quantities eg proteins triglycerides and carbohydrates
  • micronutrients are essential for normal functions. Require relatively small amounts eg vitamins and minerals
43
Q

Define metabolism

A

All the chemical reactions that occur within a living organism to maintain life.
Includes breakdown of substances to yield energy (hydrolysis and respiration) and synthesis of large molecules that are necessary for life (condensation)

44
Q

Explain reaction rates and digestion

A

Chewing food increases its surface area speeding up digestion

45
Q

Explain solubility and digestion

A

food consists of polar and non polar substances. Polar digested in aqueous acid solutions in the stomach but non polar digested in non polar environment of the intestines

46
Q

Endo/exo for condensation and hydrolysis

A

Condensation reactions tend to be endothermic, requiring energy to form larger molecules
Hydrolytic reactions tend to be exoteric releasing energy as bonds are broken in the formation of smaller molecules

47
Q

Define enzymes

A

Biological catalysts that accelerates the rate of chemical reaction in cells

48
Q

Optical isomers and enzymes

A
  • All enzymes in the body are chiral and many substrate molecules have more than one chiral centre, specific interactions with enzymes
  • The enzyme can distinguish between the enantiomers of the chiral substrate as enantiomers have different 3D shapes
  • Only one enantiomer might fit the active site so only one is biologically active
49
Q

Induced fit

A

The active site changes slightly to accomodate to the substrate. The products leave the enzyme and the enzyme returns to its original shape

50
Q

difference between cofactor and coenzyme

A

A cofactor is a metal ion or another nonprotein organic compound called a coenzyme

51
Q

Role of coenzymes

A

Interact with the enzyme during hydrolysis and act as a carrier of electrons or specific groups of atoms. Change the surface shape of the enzyme and the binding properties of the active site to better interact with the substrate.

52
Q

Enzyme in temp above optimum

A

Increased kinetic energy of the molecules, increased movement throughout the enzyme causes breakages of intermolecular forces. Disrupts tertiary and quaternary structures. Causes change in 3d shape of active site

53
Q

ENyme in temp below optimum

A

Particles have less kinetic energy so less frequent collisions with insufficient energy to overcome the activation energy barrier

54
Q

Compare GI of amylose and amylopectin

A

Amylose is a non branched polymer of glucose and not easily hydrolysed while amylopectin is a branched polymer of glucose and is soluble in h2o as can’t cil so easily hydrolysed, high GI

55
Q

GI

A

Glycaemic index. Measure of the rate of hydrolysis of carb in food
Foods contain carbs compared with pure glucose which has 100 gi

56
Q

Role of bile in hydrolysis of fats and oils

A

Bile contains an emulsifying agent with converts big fat globules into small droplets, increase SA therefore polar enzymes can hydrolyse fats easily, increasing rate of reaction

57
Q

What causes rancidity

A

C=C double bonds are susceptible to chemical reactions such as oxidation sheer polyunsaturated lips can be oxidised to form short chain ketones and aldehydes and carbolic acids.
prevented by addition of antioxidants

58
Q

Product of rancidity

A

Free radicals are small molecules with unpaired electrons that are formed by this press

59
Q

Why is energy from combustion greater

A

incomplete absorption of food by body
Incomplete oxidation of some nutrients
Heat loss, some energy released by oxidation of glues is lost as waste heat

Year 12 Chemistry (9 decks)

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